Temperature control instrument



May 18 1943 5 JQNES 2,319,406

tTEMPERATURE CONTROL INSTRUMENT 7 Filed Oct. 16, 1941 2 Sheets$heet 1 INVENTOR.

FIGZ. E 69 so 6 HARRY S. JONES y 1 H. s. JONES 1 TEMPERATURE CONTROL INSTRUMENT Fil ed Oct. 16, 1941 ZSheets-Sheet 2 9| IOB I06 00. u. 05 .03 24 nonn 27 o o o o J77. o c o I] 25 IOO FIG5.

' INVENTOR.

HARRY s. JONES ORNEY Patentecl May 18, 1943 UNITED" STATES PATENT OFFICE 3,319,406' I TEMPERATURE CONTROL INSTRUMENT Harry S. Jones, Washington, D. 0., assignor to The Brown Instrument Company, Philadelphia, Pa., a corporation of Pennsylvania Application October is, 1941, Serlal No. 415,252

The present invention relates to automatic control apparatus and more particularly to automatic control apparatus of the type in which there is provided follow-up to effect proportionate control of a supply of a condition varying medium and in which this control is eflected to give a response that is proportional to the date at which the condition under control is changing.

An object of the invention is to provide auto 7 Claims. (Cl. 250-415).

' operating condition such, for example, as a matic control apparatus of the type referred to 10 above wherein the primary controlling element is a highly sensitive device having a delicate actuating member and one in which the adjust-= merits of the control device ior regulating the supply pf a condition varying agentare efiected in response to actuation of said actuating memher without placing any restraining force upon the same. By imposing no work on the primary controlling element precision of its actuating element is assured. The specific object oi the ingo 'vention is to provide an apparam of the type in which there is a follow=up mechanism which will effect proportional control of the condition varying medium and which control takes into account the rate at which "the condition is varying. Such as a control will uickly bring heels to the control point any condition which is varying from said point. This is acomplished since ii the condition is changing quickly a larger control effect will be given to the controlling medium than if the condition is changing more slowly.

In the prior are most automatic controlling devices which are adapted to effect proportional regulations to the supply of the condition changing agent were limited to arrangements wherein the primary control element was forced either p to do some worl; and thereby reduce its sensitivity or was clamped and then had some relay mechanism perform the control function. Fursponsive.

thermore, when rate response was added to the ordinary control of the prior art this meant that a highly complicated mechanical or electrical arrangement was necessary.

In accordance with the present invention a highly developed type of control in which both follow-up and rate response are used to adjust the supply of a condition changing agent with-q; out in any way affecting the movement of the primary measuring element. In the preferred form of the invention provisions are included for readily eliectiri'g a throttling range adjustment wherebythe extent of the control device is ad,-

'iusted in response to a given change in the condition. There is also provided a means for effectchange in the load oi a furnace to bring the condition back to its normal value without affecting the rest of the control system.

- The variom ieatures of novelty which characterize this invention are pointed out with particularity in the claims annexed to and forming a part of this specification. For abetter understanding oi the invention, however, its advantages and specific objects obtained with its use, reference should he had to the accompanying drawings and descriptive matter in which is illustrated and described a preferred embodiment of the invention.

In the drawings:

Fig. i is a diagrammatic representation of a preferred embodiment oi my invention;

Fig. 2 is a diagrammatic drawing showing a top view oi the optical system;

3 is a view showing modified form of controlling a temperature condition, and more particularly, the temperature within the interior of a furnace *l' to which a thermocouple 2 is re- The supply of heating agent or fuel to the furnace is controlled by a valve 3 which is adapted to be adjusted in a plurality of positions under control of the thermocouple 2 and thereby in response to changes in the temperature within the furnace l.

The thermocouple 2 is connected by conductors 4 and 5 to the terminals of the movable coil of a suspension type galvanometer indicated generally at 6. .The galvanometer 6 is a highly sensitive measuring instrument capable of responding to extremely weak electric current flows in the conductors l and 5, and is utilized in accordance with the invention to control the selective actuation of an electric circuit indicated generally at l. The manner in which the galvanometer l is utilized for effecting such control .is illustrated ditically in Figs'l and 2. ing a rheostat adlustment of a change in an The electric circuit 1, in turn, controls the selective actuation of a relay 8 and thereby controls the operation of a reversible electrical motor 9. The motor 9 positions the valve 3 and also operates a follow-up mechanism. The follow-up mechanism, in turn, controls the operation of the circuit 1 and relay 8, providing a true follow-up control system.

The valve 3 is opened and closed by motor 9 which is selectively controlled for rotation 'in one direction or the other by field windings i5 and I6, the arrangement being such that when only the field winding I5 is energized, valve 3 is adjusted towards its open position, and when only the field winding i6 is energized, the valve 3 is moved toward its closed position.

The shaft of motor 9 is also operatively connected with a contact it which is disposed in engagement with a slidewire resistance 58, and is adapted to adjust that contact along the length of the resistance it whenever it operates to adjust the position of valve 3. The contact ll and slidewire resistance is are connected in the follow-up arrangement id referred to hereinbefore, and for convenience will hereinafter be referred to as the follow-up potentiometer. When the valve 3 is adjusted toward its open position,the contact ill is moved toward the right.

The relay generally designated at 8 includes a pair of coils i3 and 23 which are disposed in operative relation with a balanced armature 2i.

Armature 2! is pivoted for rotation at 22, a point intermediate its ends, and carries an iron core 23 at one end, which core is adapted tomove into and out of coil 93, and carries an iron core 2d at the other end, which 'core is adapted to move into and out of the coil 23. Armature 2i also carries a switch blade 25 which is disposed between a pair of stationary contacts 25 and 2?. When the coils i9 and 2d are equally energized, the switch blade 25 isheld intermeondary winding 28. The upper terminal of relay coil i9 is connected to a tap 36 intermediate the terminals of winding 28 through a circuit which may be traced from said upper terminal to a conductor 31 through the anode tocathode resistance of the triode section A of a twin type. electronic valv 33 which also includes a triode section B, a conductor 39 to a tap 40, which is adjustable along a slidewire resistance 42, resistance 32, and a conductor 53 to the tap 35 on transformer secondary winding 23. As shown, the transformer secondary winding 32 is con--' nected across the terminals of the resistance 32.

It is noted the portion of the secondary winding 23 to the left of the tap 36 is so wound with respect to the rest of the winding and with respect to the secondary winding 32 that the polarities of the voltages during one half cycle are as shown. The upper terminal of relay coil Ed is connected to the tap 36 on windinglt through a circuit including a conductor 34, the anode to cathode resistance of the triode B of valve 38, the conductor 33, tap dd, resistance 32, and conductor d3.

- Whenthe triode sections A and B of valve 33 are equally conductive, the relay coils i3 and 2d are energized to the same extent and consequently the relay switch arm 25 will be held in an intermediate position out of engagement with both of the contacts 26 and 2?,but when one triode section A or B' is more conductive than the other, the relay coil 83 or 23 will be energized to a greater extent depending upon which triode section is more conductive.

diate and out of engagement with both of the contacts 26 and 27, but when one' of the coils l9 or 29.15 energized to a greater extent than the other, the switch blade is moved into engagement with the contact 26 or 23 respectively. Electrical power is adapted to be supplied the reversible motor 9 through the switch blade 25 andcontacts 26 and 21 of relay 8 from alternating current supply conductors L and L As illustrated, the right end of the field windings l5 and it of motor 3 are connected together and to the supply conductor L The other end of the field winding i5 is connected to the contact 2'5 and the other end of the field winding 16 is connected to the contact 26. The switch blade 25 of relay 8 is connected to the supply conductor L so that on deflection of the switch blade into engagement with thecontact 23, en-

ergizing current is supplied the field winding 86 winding connected to the alternating voltage supply conductors L and L and secondary windings 3|, 32, 33 and 34. To this end the lower terminals of relay coils l9 and 20 are connected together and are connected by a common conductor 35 to the right end terminal ofthe sec- As illustrated, the triode section A includes an anode 35, a control grid 35, a cathode All, and a heatingfilament Q3. The triode section B sim-' ilarly includes an anode 63, a control grid en, a cathode 5i and a heating filament 52. The heating filaments Q3 and 52 may be connected in parallel as shown and receive energizing current through conducting leads, not shown in order not to confuse the drawing, from the transformer secondary winding 36. Anode voltage is supplied the triode sections A and B through the energizing circuits traced above for the relay coils l3 and 20.

The grid circuit for the triode A maybe traced from the grid 33 to a conductor 53, in which a current limiting resistance 53 is inserted to the left end terminal of winding 28, tap 36, conductor 43, resistance d2, tap 50, and conductor 33 to the cathode 61. It is noted the winding 32 and the portion of winding 28 to the left of tap 36- are so phased as to oppose each other, the winding 32 tending to. render the grid 46 negative with respect to cathode 51 during the half cycle when the anode fldis positive and the portion of winding 23 referred to tending to render the grid 58 positive with respect to cathode 47 during the same half cycle. Whether the grid at is at the same potential as cathode 61 or positive or negative with respect thereto'is determined by the adjustment of contact 40 along resistance 42. It is noted the potential of grid 46 is substantially constant during the normal operation of the system.

The grid circuit of the triode B may be traced from the grid 53 to a conductor 55, in which a current limiting resistance 53 and a resistance 51 shunted by a condenser 58 are inserted, to the resistance 32, tap 40 and conductor 39 to the cathode 5|. The potential of grid relatively to cathodeil is adapted to be varied in accordance with the illumination of a photoelectric cell neoted in the circuit that the polarity-of the potential drop established is that shown. The energizing circuit'for cell 55 may be traced from the right end terminal of winding 25 to conductor 35, cell conductor 55, resistance 51, and conductor 43 to the tap 38 on windingit. The illumination of cell 58 is controlled by the galvanometer 5 in response to variations of the temperature within the furnace I by means which are described hereinafter.

The adjustable resistance 42 is included in a connection which is common to the grid circuits of both triode sections A and B so that adjustment thereo! cpeiates to simultaneously change the potentials of the grids 46 and 50 relatively to their associated cathodes. It is noted that adjustment oi the contact 50 in the direction to include more or the resistance 42 in circuit is eiiective to render the grids more negative with respect to their associated cathodes while adjustment of the contact 40 in the opposite direction is effective to render the grids less negative withrespect to their associated cathodes. The contact 4t desirably is adjusted so as to suit the characteristics "of the triode sections A and diagrammatically in Figures 1 and 2.

thereby establish the most efficient operatthe position or the shield at and lens 69 is adjustable by an arrangement described hereinafter.

In the normal operation of the system the triode sections A and B of valve 38 are equally conductive when the illumination of the photoelectric cell 59 is a predetermined value. Under this condition, the relay coils l9 and are equally energized and consequently the motor 9 is not actuated for rotation in either direction and remains stationary. Upon slight movement of the vane 68, for example, in a clockwise direction in Figure l in response to a decrease in furnace temperature from the desired value the illumination of photoelectric cell 59 is substantially increased whereupon the grid 50 is rendered less negative in potential with respect to its associated cathode 5| and consequently the conductivity of the triode section B is'lncreased. This causes an increase in the energization of relay coil 20 and as a result the relay switch blade is actuated into engagement with the A. light aluminum vane 8'6 which is impervious to light is disposed on the end of the pointer The galvanometer 6 is so arranged with respect to the photoelectric cell 59 and with respect to a source of light, such as a lamp 6i, that the vane 66 is adapted to be motivated into and out of the path of the light impinging on photoelectric cell 59 in accordance with the deflections of the movable coil thereof and thereby in accordance with the furnace temperature variatlons. ceives energizing current from the transforme secondary winding .13.

As illustrated, an opaque plate 68, in which a focusing lens 8 is mounted, is also positioned between the photoelectric cell 59 and lamp 51, and the optical system is so arranged that the only llghtirom'lamp 81 which is permitted to impinge on cell 58 is that which is transmitted by the lens 8!. The lens 89 and the length of the salvanometer pointer SI are so proportioned that the vane 56 is adapted to move into the path of the light impinging on cell 5! at approximately the point of icons on the lens 0!. Thus. arslight movement of the vane 86 in one direction or the other is suiiiclent to fully illumiunto the cell I! or to cut oil! all of the light thereto. In accordance with the present invention,

The lamp 81 is connected to and recontact 21 to thereby close the energizing circuit for motor field winding l5. The motor 9 is then operated for rotation in the direction to chest an opening adjustment of the fuel valve 3.

Upon slight movement of the vane 66 in the counterclockwise direction in response to an increase in furnace temperature from the desired value, the illumination of-the photoelectric cell 59 is substantially decreased, whereupon the grid 58 is rendered more negative in potential with respect to the cathode 58 to thereby reduce the conductivity of the triode section B. This effects a decrease in the energlzation of relay coil 26 and consequently actuation of the switch blade 25 into engagement with the contact 25 and thereby closure of the energizing circuit to motor field winding it. The motor 9 is then actuated in the direction to produce a closing adjustment of the fuel valve 3. As noted hereinbefore, rotation of the motor 9 to effect a fuel valve adjustment also effects an adjustment of the follow-up potentiometer ill, is.

It is noted that deflection of the galvanometer pointer cu in the counterclockwise direction of an amount to cause the vane 66 to move complete- 1y through the light beam and thereby permit illumination of photoelectric cell 59 even though the iurnace temperature is higher than the desired value is prevented by the vane 66 striking against a stop it.

In accordance with the present invention, adjustment of the follow-up potentiometer l1, l8 eflects an adjustment of the plate '68 and lens 59 relatively to the lamp 5'! and photoelectric cell 59. Such adjustment effects a transverse shift in the focal point of the light beam impinging perature within furnace l.

resistance l8.

, the heaters will be bimetallic elements 12 and 13 are electric heatera 15 and 18 respectively which are electrically connected at their upper ends by a wire 11 that is connected to the left hand end of transformer secondary coil 3!. ilhe electrical circuits for the heaters are completed through a wire is and a resistance i9 that can be varied by means of a slider N which serves a purpose to be later described. From the resistance 19 a connection is made to the slider ii for the potentiometer resistance it. Heaters l and it are connected respectively through resistances 8i and 82 which can be adjusted by means of sliding contacts 83 and 86. These resistances serve a purpose which will be described below.

' From the above description it will be seen that as the slider ii is moved to the right or to-the left more or less of the resistance it will be put into the circuit containing the heaters and it. In this manner the bimetallic strips will be heated to different degrees and will serve to and conversely rotation of the knob 85 in the other direction operates to decrease the amount of resistance 82 and to increase the amount of resistance 8i in the heater circuits respectively.

By reason of the above construction a true follow-up control system is provided. Upon an increase in the temperature of the furnace i, the

the valve 3. This operation of the motor also effects an adjustment of the contact ll along the resistance it to the right. Such a movement of the contact I'i will cause an increase in the heat produced by the heater l5 and a decrease in the heat produced by the heater it thereupon causing the bimetallic strip E2 to warp in such a fashion that the lens 69 is moved to the right in Fig. 1. When the lens has been moved an amount to restore illumination to the photoelectric cell 59 to a degree in which the sections A and B are equally conductive, the

motor 9 is deenergized and the system is-stais operated in a direction to open the fuel valve and the contact I! is moved to the left along The resistance 19 permits an adjustment of the throttling range of the system so that the amount fuel valve 3 is adjusted in response to a given change of temperature may be varied.

' For example, upon an adjustment of the contact 80 in a direction to decrease the amount of resistance 19 in the circuit, the voltage applied to increased whereby a smaller adjustment of the contacts ll along the resist ance II will be required to effect the follow-up The operation of the system for action of the lens 69 to restore the illumination to the cell 59 to a value at which the motor ,1: is

deenergized. Accordingly a small fuel valve adjustment will be made for-a given furnace 5 temperature change. An adjustment of the contact tt'along the resistance 19 in a direction to increase'the amount of the resistanceof the circuit will have the opposite effect upon the operation of motor 9.

The portion of adjustable resistances BI and 8:2 inthe follow-up arrangement permits a so" called reset adjustment of the system so that on a change in the operating condition of the furnace i, for example, on a change in the load 7 .thereof, or on a change in the B. t. 11. content of the fuel being supplied thereto, the tendency of said load change, fuel heating valve change,

or other operating condition change, to increase or decrease the furnace temperature may be neutralized. As explained hereinbefore, the

resistances 8i and 82 are adapted to be simultaneously adjusted in opposite directions by manipulation of the knob 85. Such manipulation of knob 85 operates to change the initial position of support ii and thereby the position of lens 69, for a given position of contact it along resistance l8, and thereby operates to change the relation between the position of the lens 89 and the adjustment of fuel valve 3 for a given furnace temperature value at which the motor 9 is not energized for rotation in either direction. Accordingly, on such manipulation, the motor 9 is energized for rotation to efiect an adjustment of fuel valve 3 and an adjustment of contact ll along resistance it as required to restore the lens 59 to the position in which the motor 9 is deenergized for rotation. I'hus, the provision of resistances BI and d2 permits load compensating or reset adjustments to be read- 40 ily made.

As will be apparent to those skilled in the art, the provision of the adjustable resistances i9, 8i and B2 permits of a wide range of variation in the furnace operating characteristics thereby permitting a desirable good regulation under very different conditions of operation. The speed with which the lens 59 is shifted as a result of a change in the temperature of the furnace i will have an effect on the amount of change in the valve opening. If, for example, the bimetallic strips and the heaters are so designed that they act quickly as a result of a movement of a given movement of the contact it along resistance It a comparatively small'adjustment of the valve 3 will take place before the photoelectric cell 59 has the proper amount of light again upon it. If, on the other hand, the heaters and the bimetallic strips are so designed that the lens 69 will move slowly then there will be a commaratively large adjustment of the valve 3 before the photoelectric cell is again properly lighted. Thus it will be seen that if the strips 12 and I3 and the heaters 15 and 16 are properly designed for the lag in the condition being measured or Us the furnace characteristics that there will be a correction givenin proportion to the rate with which the temperature is changing.

In the normal operation of the device, the lag .in time between when the motor 9 is energized 70 and when the heater 15 or 16 has become hot enough'to move the lens 69 sufficiently to produce deenergi'zation of the motor will be enough to cause on over-correction of the valve 3. During this time the lens 89 will have been moved to such an extent relative to the vane Bl that the respect to the galvanometer 6 so will intercept the light to the photoelectric of a, transiormer 8 I.

motor will be energized for rotation in the opposite direction to back oi! the valve adjustment to the proper place. At the same time the current in the heaters I5 and I6 will be correspondingly changed so that the lens 69 will be slowly moved back to its correct position for the furnace tem perature. If the rate of heating of the bimetallic strips is properly related to the rate of heat change of the furnace in response to fuel changes, the over-correction and backing oil of the valve will be suflicient to quickly return the value of the temperature in the furnace to normal. If the temperature is changing at a faster rate the valve and the slider Il will be adjusted more before the lens has moved su'fllciently to produce deenergization of the motor than it would if the temperature hadelonly deviated a small amount.

t will, therefore, be seen that the arrangement disclosed above not only gives a proportional movement of the valve for each change in temd in order to change the control point of this instrument, or the normal temperature which the instrument tends to maintain in the furnace I, it

is necessary to shift the photoelectric cell 58 with so that the baiile cell at some other point. Generally speaking, in

an instrument of this type the photoelectric cell 55, thelight til, the stop in and the lens supporting bracket i l will be mounted together on asupport which'swings around a pivot coaxial with the galvanometer suspensions. In this fashion, as will be seen from Fig. 2, the photoelectric cell and the lens will be changed relative to the baiile 66 so that in order for the cell 69 to get the proper amount of light the baiile will have to be at some other position.

In Fig. 3 there is shown a modification. of the invention in which there is provided a concave mirror 35 on the-galvanometer d in place of the pointer E30 and the baffle 8t. Light from the lamp S'i is directed toward the mirror through a lens M which is rigidly mounted in a support 88 that is carried by the light supporting bracket it. From the mirror the light is reflected on to the photoelectric cell 59. Therefore, any deflection of the galvanometer will shift the light "beam away from the photoelectric cell thus causing a differential heating of the'heaters I5 and it.

Such action of the heaters will shift the light Bl in a direction so that its beam of light can again be deflected upon the photoelectric cell 59.

c This operation of the light Bl also gives the follow-up movement of the control instrument that was obtained in Fig. l by movement of the lens 69 independently of the light. The speed with which the light 6! is shifted to one side or the other gives a rate response to the control instrument similar to that described in Fig. 1. This arrangement otshifting the light with the lens accomplishes the same results that have been ent manner. In some cases it is possible that this arrangement may be preferable to that shown in Fig. 1. v I I In Figure 4 there is shown another embodiment of the invention in which only one electronictube is used and in which the photoelectric cellis shifted ratherthan the lens. The

single electronic tube 89 in this embodiment has.

its filament heated from a secondary winding previously described except in a slightly diflertube extends from the plate 92 through a heater 93, that acts on a bimetallic element 94, to the right end of a transformer secondary winding 95. A tap is taken from this winding at 96 and is connected through wire 91 to cathode 98. The

"cell 59 extends from the right end terminal of the transformer secondary winding 95 through the cell 59 to the resistance Hill and back to the transformer. The cell 59 is, in this case, also connected so that current flowing through it will cause'a potential drop across the resistance 08. The magnitude of this drop will depend upon the light falling on the cell.

As the photoelectric cell. 5%? is moved by the bi metallic strip 9 3 it sh fts a contact 503 along a resistance I043, which resistance forms two legs of a bridge circuit that is energized from a transformer secondary winding I05. The other legs or the bridge circuit are formed by the resistance Ito that is engaged by a movable contact iol which is connected to the other side of transformer winding I'l /5. Connected between each end of the resistors GM and 1% are coils I08 and H09 that are variably energized depending upon the positions of the contacts IE3 and iill. Cooperating with the coils Hi8 and W9 are cores 23 and 2% that are attached to a rocking switch carrying arm such as was used in the embodiment oi Figure 1. As one of the coils is energized morethan the other, the contact 25 will be brought into engagement with. contact 26 or El to energize motor 9 for rotation in one direction or the other. The motor, in this case, simultaneously adjusts the valve 3 Mil along the resistance G69.

In the operation of this modification of the invention the flow or current for one half cycle will be as indicated by the symbols on the drawing. At this time, if the temperature is at its normal value, the galvanometer pointer will be in the position shown and a portion of the light from lamp I5? will fall on the cell 59. A small amount of current will then flow through the cell and the plate circuit of the tube 89 will pass enough current to the heater Q3 so that the bimetallic element will hold the photoelectric cell in the position shown. Upon an increase in the temperature of the furnace, vane will move in a counterclockwise direction or downwardly to cut oil? more light to thereby reduce the current flow through the cell 59. Accordingly the grid as will become more negative and less current can flow through the plate circuit to the heater 93. As a result of this the bimetallic strip 96 will cool off and move the cell 59 downwardly until the proper amount oi light again falls on it to hold the cell in its position.

Movement of the cell 59 causes a movement of contact I03 along resistance I06 in the same direction. If the bridge circuit was balanced, the

downward movement of the contact I03 will unbalance it in such a direction that coil I09 will become more energized than coil I08. As a result of this the core 23 will be pulled to the left bringing contacts 25 and 26 into engagement to energize the motor field I6 for rotation to close the valve 3. While the valve is being closed the The plate circuit of this and the contact shown in Fig. 1.

is shown a concave mirror 86 of the type disclosed contact i! is being moved upwardly along rethat the temperature will be quickly brought back to normal.

The embodiment of the invention shown ;in Fig. corresponds very closely to that of Fig. 1 in that the same heater control circuits are used for the two heaters i5 and 78 in Fig. 5 as those In this, case, however, there in Fig. 3 so that upon a movement of the salvanometer coil light will be reflected from the lamp 6?, by this mirror, to the photoelectric cell 59.

In this embodiment of the invention the galvanometer coil is suspended by two bimetallic suspension elements lit and iii each of which;

when it is heated, tends to turn the galvanomeaaraeoc H1 at a restricted rate that is governed by the setting of a, tapered screw H8 which cooperates with a valve seat H9 formed at the right end of the opening Ill.

The transformer 29 in this case is provided with ,a secondary winding I that is connected in a series circuit with a solenoid |2l which surrounds the upper part of the chamber H4. This circuit also includes a current limiting resistance U22 and a variable resistance I23. A contact I24 is slidable along thelatter resistance to regulate the amount of it in the circuit and is ter coil in opposite directions. The heaters l5 and i6 areassociated with suspensions H0 and 1 iii respectively. With this embodiment,as.the

contact I? is moved by motor 9 relatiye'to the I resistance IS the amount ofcurrent flowing through the heaters and i6 is varied. This causes one of the suspension elements H0 or ill to be heated more than the other so that the flected to reflect, for example, more light on the photoelectric cell. 59. In response to the light on the cell, triode section B of the tube 38 will be made more conductive than the section A so that motor 9 will be energized for rotation in the proper direction to readjust the valve 3 to bring the temperature of the furnace back toward normal. This same rotation of the'motor 9 will shift contact iialong resistance i8 and vary the current flowing .through the heaters 75 and T6 in such a manner that the galvanometer coil 6 will deflect in a direction to reflect a smaller amount of light upon the cell 59.

If the rate at which the suspension elements iii! and iii warp is correlated with respect to the constants of the furnace 2 and the galvanometer, the latter will be deflected in such a fashion that it will compensate for the rate at which the temperature in the furnace is chan ing. If the temperature is changing fast, a large movement of the contact I! will take place before the heating has an effect on the galvanometer suspensions, so that the motor will cause the valve to over-travel. Therefore, the galvanometer will deflect to such an extent that it will reflect less light on the photoelectric cell thus causinga backing off movement of the valve, and of the galvanometer, to bring the temperature to its normal value quickly. As the temperature is returning toward its normal value the galvanometer will be slowly moving toward 7 its normal position and a state of balance will be reached with the galvanometer deflecting properly and the temperature at the .control oint. p The embodiment of the invention disclosed in Figure 6 difiers from those previously described in thatthe rate response or, in eflect, the delayed follow-up is procured by means of a dash-pot rather than from heating coils. In Figure 6 the lens H2 is mounted on a stem that is attached to ance in the circuit of solenoid I2I.

moved by the motor 9 while the valve 3 is being adjusted, as was contact il in Figure 1.

In this embodiment of the invention the lens H2 and the float H3 must move in a vertical direction, so in order for the vane 66-to properly cut the light it must also move in a vertical direction instead of horizontal as shown in the an electronic circuit and a relay circuit such as are shown'at i and 8 respectively, in Figure l are used. Thus, when the temperature of the furnace 1 decreases the galvanometer will deflect upwardly to permit more light to fall on the photoelectric cell 59. This operates to make the grid of the triode section B less negative so that more current will flow in the plate circuit and through the coil 29. The energization of the coil 20 operates to move contact 25 into engagement.

with contact 21 energizing motor fleld i5 so that the motor will open valve 3. As the motor rotates it will also shift contact i2 3 to the right along resistance I23 to place more of that resist- Such a movement of contact I24 decreases the energization of the solenoid i2land permits the float H6, which normally sits higher in the liquid in chamber H4 than is shown, to rise and move lens H2 upward. This movement shifts the path of the beam of light so that it is again partially blocked by the vane 66 to give the follow-up movement.

In this case the speed of th follow-up movement is determined by the rate at which the liquid in chamber I It can pass through the passage ii'iinto the cylinder H5 below piston xi i6. Whether the follow-up movement is upward or downward the speed at which it takes place depends upon the adjustment of the resistoriiiii. Due to the delayed follow-up, the motor 9 will be energized an amount of time sufllcient to give an over-correction to the valve 3 and will move contact H24 tothe right enough so that the lens H2 will rise high enough so that vane 66 will cut off more light than is necessary for equilibrium of the electrical system. As a result the motor will be run in a reverse direction far. enough to remuch on the other side of itsnormal value.

over-correction of the valve.

move the over-correction given to-the valve 3, as the temperature returns to normal.

It will be seen from the descriptionthat has been given above for the various embodiments of the invention, that in each case there is a delay in the follow-up action which is given as a result of a change in temperature of the furnace I. When a change in temperature occurs the galvanometer pointer in each case is moved a corresponding amount. This movement changes the light falling on photoelectric cell 59 to change the current flow through the triode section B. As a result of this, one of the solenoids I5 and 29 becomes more energized than the other to run the valve operating motor 9 in one direction or the other to correct the temperature variation. This same operation of the motor changes the heating effect on the bimetallic elements of Figures 1 to 5 inclusive and changes the energization of the solenoid 12! in Fig. 6 so that a follow-up movement will occur to stop the operation of the motor.

In ordinary control systems, this follow-up movement is contemporaneous with the adjustment of thevalve so that there is no over-correction of the valve. In the present application, the follow-up movement is delayed so that there is always an over-correction of the valve and an over-adjustment of the contact controlling the heaters for the bimetallic elements and for the solenoid l2l. Due to the fact that the valve is adjusted more than is necessary for a given temperature change, the temperature of the furnace will quickly return toward normal. If this over-correction of the valve is not removed the temperature of the furnace would swing too As a result of the over-correction, therefore, it is necessary to reverse the operation of the valve operating motor. ihis reversal takes place because of the fact that in each of the embodiments the follow-up movement is greater than is necessary for the particular position of the galvanometer pointer. Therefore, the valve motor is run .in the opposite direction to reduce the At the sam time that this over-correction of the valve is being removed and the over-correction of the follow-up is being removed, the temperature of the furnace has begun to return toward normal. For example, in Fig. 1 when the lens 69 is being moved back toward its normal position the galvanometer pointer is also moving and the parts return toward their normal positions at approximately the same rate so that the final adjustment of the valve is sufficient to take care of the Original temperature change as the parts return to their normal positions. It will be seen that if the temperature change is fast the valve will be operated a greater amount before the bimetallic elements have, for example, heated sufiiciently to give the follow-up movement, Whereas if the temperature change is very slow the bimetallic elements will be heated slowly and there will be no appreciable overshooting of the valve adjustment.

Since the heating constants of the bimetallic elements, and the adjustment of the screw H8 which restricts the flow of the liquid in the embodiment of Fig. 6, are adjusted in accordance with the characteristics of the furnace whose temperature is being controlled, it will be seen that the control of this application will take into account not only the amount and direction of the temperature change but also the rate at which the temperature changes. This means that a larger correction is given ifthe temperature is changing rapidly ,than'would'be given if the temperature was changing slowly. Therefore, the temperature offlthe furnace I will always be brought back to its normal value quickly and with a minimumamount of hunting.

While in accordance with the provisions of the statutes, I have illustrated and described the best. form of this invention now known to me, it would be apparent to those skilled in the art that changes may be made in the form of the apparatus disclosed without departing from the spirit of this invention as set forth in the appended claims, and that in some cases certain features of this invention may sometimes be used to advantage without a corresponding use of other features.

Having now described my invention, what I claim as new and desire to secure by Let ers Patent is:,

1. In a control instrument, the combination of means to produce a path of radiant energy, a device operative in response to variations in the radiant energy, a first member deflected in response to variations in the value of a condition to be controlled to vary the amount of radiant energy applied to said device, a second member also movable to vary the radiant energy applied to said device and operating in opposition to said first member, an electric circuit varied by said device in response to variations in radiant energy applied thereto as said first member moves, mechanism operative by electric circuit changes to move said'second member in a direction to neutralize the effect of said first member, said mechanism including a part operative to delay the neutralizing action an amount or time proportional to the rate of deflection of the first memher.

2. In a control instrument, a means to produce a path of radiant energy, means responsive to variations in the value of the radim'it energy in said path, an electric circuit controlled in onedirection or an opposite direction by said responsive means as more or less radiant energy falls thereon, a member deflecting in response to variations in the value of a condition to be controlled and operating as a result of said dcflections to vary the amount of radiant energy reaching said responsive means, a device movable to counteract the eifect of said member on said radiant energy path, means operated by changes in said electric circuit due to deflections of said member to move said device, said device including a part to delay the counteracting effect for a time proportional to the rate of change of the condition.

3. In a control instrument, a means to produce a beam of light, a light responsive element upon which said beam is directed, an electric circuit in which said element is connected and which is changed in one direction or the oppost direction as more or less light falls on said element, a

- member deflecting in response to variations in the value of a. condition, and operative to vary the amount of light falling on said element in accordance with the deflections thereof; a device operative to counteract the efiect 01' said member ment as it warps to act on said beam of light in a manner opposite to the action of said member.

4. In a control instrument, a means to produce tions in the value of a measurable condition and operating to vary the light falling on said cell in accordance with the deflections thereof, a device acting to counteract the eflect of said deflecting member comprising a bimetallic element and a heating coil therefor, means operated by said cell in response to a change in light falling thereon to produce a heating of said coil whereby the bimetallic element will be bent, the delay in action of the heating coil and bimetallic element producing an over-correction of the counteracting effect, and means moved by said lbimetallic element to act on said beam of light in a manner opposite to the action of said member.

5. In a control instrument, means to produce a beam of light, a photoelectric cell responsive to variations in light and upon which said beam is directed, a lens to direct light to said cell, a member deflecting in response to variations in the value of a measurable condition and acting to beam of light in a direction to counteract the eflect oi the deflectable member.

6. In a control instrument, means to produce a beam of'light, a photoelectric cell upon which said beam is directed andwhich is responsive to variations in the light reaching it, a member deflectable in response tovariations in the value of a measurable condition and operative to vary the light falling on said cell, a lens to direct the light to the ceILVmeans to shift said lens to change the path or the light beam; 9. device for moving said lens, means operative in response to a change in value of the light falling on said cell as said member deflects to shift the lens and therefore the direction of the beam of light whereby the light will fall in its original amount upon the cell, and means to vary the rate at which said lens will be shifted in accordance with the rate of change of the condition.

7. In a control instrument, means to produce a beam of light, a photoelectric cell upon which said beam is directed and which is responsive to variations in the light falling theron, a member deflectable in response to variations in the value of a condition to be controlled, said member acting to vary the amount of light falling on said cell as the member deflects, a lens serving to direct light from said means to said cell, means to move said lens and thereby shift the p th 01' said beam of light in response to variations in light received by said cell as determined by the position of the deflecting member, said last named means operating to shift the lens in a direction to redirect the original amount of light on the cell, said last means comprising a part operating in accordance with the rate of change of the condition being measured. 

